Bug 262325 - Fix some help strings for UI commands (undo/redo).

ChatZilla only.
r=silver@warwickcompsoc.co.uk
p=gk1987@gmail.com (Gijs Kruitbosch)

extensions/irc/xul/locale/en-US/chatzilla.properties

@@ -93,12 +93,12 @@ cmd.cmd-docommand.help   =
 cmd.cmd-undo.label  = &Undo
 cmd.cmd-undo.key    = accel Z
 cmd.cmd-undo.params = 
-cmd.cmd-undo.help   = Copies the currently-selected text to clipboard.
+cmd.cmd-undo.help   = Undoes the last change made to text in the input box.
 
 cmd.cmd-redo.label  = &Redo
 cmd.cmd-redo.key    = accel Y
 cmd.cmd-redo.params = 
-cmd.cmd-redo.help   = Copies the currently-selected text to clipboard.
+cmd.cmd-redo.help   = Redoes the last change to the text in the input box which you undid.
 
 cmd.cmd-cut.label  = Cu&t
 cmd.cmd-cut.key    = accel X